The heart of a computer is a magnetic hard disk drive (HDD) which typically includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and/or write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The volume of information processing in the information age is increasing rapidly. In particular, HDDs have been desired to store more information in its limited area and volume. A technical approach to this desire is to increase the capacity by increasing the recording density of the HDD. To achieve higher recording density, further miniaturization of recording bits is effective, which in turn typically requires the design of smaller and smaller components.
The further miniaturization and improvements to performance of the various components, however, presents its own set of challenges and obstacles.
In one approach, energy-assisted magnetic recording may be employed to produce a high magnetic recording density. In conventional microwave-assisted magnetic recording products and applications, the typical magnetic recording is based on superposing an assist magnetic field and a write magnetic field. In order to adequately improve the performance of MAMR products, each of the assist magnetic field characteristics and the write magnetic field characteristics may be enhanced.
In order for a large current to flow efficiently to a spin torque oscillator (STO) of a MAMR head, the back gap-side current path must be electrically insulated. With this in mind, alumina (Al2O3) is typically employed as the back gap material. However, because alumina is a non-magnetic material, the magnetic circuit of the recording head is magnetically separated in the vicinity of the back gap. This produces a marked increase in the magnetic circuit resistance in the back gap that precludes the write magnetic field from being efficiently generated from the main pole. Accordingly, conventional MAMR structures exhibit undesirably low responsivity of the write magnetic field to the recording current.
In other conventional perpendicular magnetic recording head structures, an FeCoNi alloy may be employed for the back gap. Table 1 shows a comparison of the electrical and magnetic characteristics when alumina is employed for the back gap and when a permalloy is employed for the back gap.
TABLE 1Electric resistance of current path and response properties forconventional MAMR heads employing permalloy (FeCoNi) and Al2O3 back gap materials.PermalloyBack gap material(FeCoNi)Al2O3Resistance (Ω)  5 × 10−4  5 × 1017ΔHeff/ΔI (Oe/A)2.4 × 1051.9 × 105
These data refer to a conventional permalloy FeCoNi alloy defined by the composition Fe80Ni20. The electrical resistance when this permalloy is employed for the back gap is 5×10−4Ω, and the responsivity thereof is 2.4×105 Oe/A. The STO side resistance is 0.6Ω. Accordingly, because almost all the current flows along the current path on the back gap side, the STO does not oscillate and, no assist magnetic field is generated. Notably, because an equivalent resistivity and a saturation magnetic flux density of not less than 0.1 T is produced when FeCoNi alloys having a composition other than Fe80Ni20 are employed, this same conclusion may be drawn for permalloy-containing MAMR head structures, regardless of the specific composition.
As a result, there is little to no microwave-assisted effect produced during magnetic recording in typical structures employing permalloy as the back gap material.
On the other hand, in conventional MAMR head structures where alumina is employed for the back gap material, an electrical resistance of 5×1017Ω and a responsivity of 1.9×105 Oe/A are produced. As a result of a marked increase in the magnetic circuit resistance in the back gap as described above, a write magnetic field cannot be efficiently generated by conventional MAMR head structures employing alumina as a back gap material.
Accordingly, the responsivity of the write magnetic field to the recording current is undesirably low in conventional MAMR head structures employing alumina as the back gap material. Moreover, a microwave-assisted magnetic recording head in which the write magnetic field responsivity is improved as much as with permalloy back gap materials, while avoiding the electrical insulation characteristics of the current path in the vicinity of alumina back gap materials would be highly desirable.